In collaboration with Patrick George and Frederic Druon at the Institute
d'Optic, in France, a regenerative amplifier was demonstrated using Yb-doped
GdCOB. This laser material has a thermal conductivity 3 times higher than that
of Yb-doped phosphate glass and an emission cross-section of a similar value.
The chirped pulse amplifier produced 12 mJ pulses compressed to 30 fs.

Yb-doped
KYW is a laser crystal that exhibits an emission cross-section considerably
larger than the Yb-phosphate glass and the GdCOB used in previous experiments.
Furthermore, by using a minor axis for pumping and lasing a broader, smoother
spectrum can be made to lase. In an end-pumped configuration, the KYW crystal
produced a slope efficiency of 40% and a cw output of 680 mW from an incident
pump of 2.8 W. As a regenerative amplifier this laser produced 50 µJ pulses at
2 kHz repetition rate. Compressed, 40 mJ pulses measured 400 fs in duration.
Using the same pumping configuration and reconfiguring the cavity to include
dispersion compensation, Kerr-lens mode-locking laser was obtained. This is the
first diode-pumped rare-earth laser to be mod-locked without a semiconductor
saturable absorber. It displays a pulse duration ranging from 71 to 105 fs.

65-µJ pulses were obtained from a side-pumped version of this laser at 2 kHz
using a 20 W diode bar. Autocorrelation indicates these pulses have 460-fs
duration. In similar experiments Yb-doped KGW was used as a gain material in a
regenerative amplifier, but with the primary axis being excited (E//a). In this
laser a 43% slope efficiency was seen in cw operation and 43 µJ pulses were
obtained at a repetition rate of 1 kHz. Raman activity was also observed in this
system. Finally, a high-energy regenerative chirped-pulse amplifier was
demonstrated using a flashlamp-pumped Ti:sapphire laser as a source to simulate
diode pumping with up to 1.2 J. The slope efficiency of the laser was as high as
72% in free-running mode, without polarizer or electro-optic cell. As a
chirped-pulse amplifier, the laser produces 25 mJ compressed to 1.4 ps pulse
limited by gain narrowing. The following table summarizes the characteristics of
several Yb-doped lasers demonstrated during the last two years at CUOS.